[From pneumonic infiltration to parapneumonic effusion--from effusion to pleural empyema: internal medicine aspects of parapneumonic effusion development and pleural empyema].

Infectious processes cause the majority part of all clinically relevant pleural effusions which frequently complicate the course of pneumonia. The assessment of an inflammatory effusion requires a careful history, physical examination, imaging techniques and clinical workup. The presence of polymorphonuclear leukocytes, high LDH-activity (> 200 U/L) and protein level (> 3 g/dL) in a pleural effusion indicates acute inflammation. An effusion is usually called empyema, when large numbers of neutrophils form thick, turbid exudates within preexisting body cavities. A thoracic empyema may occur as a result of primary or secondary pleural pathologies and in most cases involves infection with bacteria, frequently provided by progressing pneumonia. There are several therapeutic options for treatment of parapneumonic effusions and of thoracic empyemata, respectively. Optimal therapeutic management and antimicrobial medication to the infected pleural space depend in part on the stage of the empyema at presentation. Treatment can vary from a conservative medical approach in uncomplicated or small parapneumonic effusions to invasive surgical interventions in fibroprulent or organizational stages of empyema. Empyemata usually progress from a parapneumonic exudative stage (stage I), when the fluid is still sterile, with low leukocyte counts, low LDH, physiological pH, and normal glucose, to the fibropurulent [figures: see text] stage (stage II) with high leukocyte counts, high LDH activity, low pH, and low glucose, and finally to the organizational stage (stage III), in which fibroblasts convert fibrin strands into inelastic membranes. Pleural peels and pockets may compartmentalize the viscous empyematous fluid and can cause serious restrictive ventilatory impairment. Each patient must be individually evaluated to determine the nature of the exudate and the stage of the pleural space infection. Due to its high mortality rate (5%) a thoracic empyema requires prompt treatment. Diagnostic thoracentesis and withdrawal of liquid for the microbiological, cytological and biochemical analysis is urgently recommended in all cases to assess severity of the disease and the likelihood of a complicated or uncomplicated course, and to select the most appropriate treatment option.